Fixing Member and Fixing Unit

The present application is a divisional of U.S. patent application Ser. No. 18/190,498 filed on Mar. 27, 2023, which claims priority from Japanese Patent Application No. 2022-063233, filed on Apr. 6, 2022, which are hereby incorporated by reference herein in their entireties.

This disclosure relates to a fixing member used for an induction heating type fixing unit and a fixing unit including the fixing member.

In electrophotographic image forming apparatuses, fixing units which heat fixing members by the principle of induction heating and fix an image on a recording material by the heated fixing members are known. This type of the fixing members includes a circumferentially continuous conductive layer, and generates heat by Joule heat which is generated when an induction current circulates around the conductive layer in response to an alternating magnetic field formed by a magnetic field generation member such as a coil.

In Japanese Patent Application Laid Open No. 2015-118232, it is described that, by dividing a heating layer (conductive layer) of a tubular fixing member into a plurality of areas (segments) in a longitudinal direction, even if damage such as cracks have occurred in the heating layer, an abnormal temperature rise is made less likely to occur in adjacent areas of the damaged portion.

In a case such as continuous image formation on a plurality of sheets of the recording material, a phenomenon (called as a temperature rise in a non-sheet passing portion) may occur. When the temperature rise in the non-sheet passing portion occurs, a temperature of an end portion area (i.e., non-sheet passing portion) where the fixing member does not come into contact with the recording material becomes higher in comparison with an area where the fixing member comes into contact with the recording material. In a case where an extent of the temperature rise in the non-sheet passing portion is remarkable, there is a possibility that, since deterioration such as wear or changes in physical properties of surfaces of the fixing member and members adjacent to the fixing member will be caused by the heat, performance or durability of the fixing unit will decrease. Further, since the occurrence of the temperature rise in the non-sheet passing portion means energy consumption in a form of not contributing to the fixation of the image, the temperature rise in the non-sheet passing portion is preferably kept to be as little as possible.

The present disclosure provides a fixing member and a fixing unit in which a conductive layer of the fixing member includes a plurality of segments and which can reduce temperature rise in a non-sheet passing portion.

According to an aspect of the present disclosure, a fixing member includes a conductive layer configured to generate heat in a case where a circulation current in a circumferential direction of the fixing member having a tubular shape is induced, wherein the conductive layer includes a plurality of segments arranged in a row in a longitudinal direction of the tubular shape and electrically separated from each other, where each of the plurality of segments is formed continuously over an entire circumference of the tubular shape in the circumferential direction, and wherein the conductive layer is configured such that a heat generation amount in an end portion of the fixing member in the longitudinal direction is less than a heat generation amount in a central portion of the fixing member in the longitudinal direction in a case where an alternating magnetic field is applied to a whole area of the fixing member in the longitudinal direction in a state where a temperature of the central portion of the fixing member is equal to a temperature of the end portion of the fixing member.

Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

Hereinafter, embodiments of this disclosure will be described with reference to drawings.

With reference to, an image forming apparatusof an embodiment (example 1) will be described The image forming apparatusis an image forming apparatus of an electrophotographic system, and, in particular, a monochrome printer of a direct transfer system. The image forming apparatusforms an image on a recording material P using toner (developer) based on image data received from an external apparatus. Not limited to a single-function printer having only a printing function, the image forming apparatus may be a copy machine, a facsimile, or a multi-functional machine combining a plurality of these functions. As the recording material P, it is possible to use various sheet materials which are different in size and materials, including paper such as standard paper and cardboard, a plastic film, cloth, a surface treated sheet such as coated paper, a sheet material of a special shape such as an envelope and index paper, and the like.

The image forming apparatusincludes an image forming unitA for forming a toner image (hereinafter simply referred to as an image) on the recording material P and a fixing unitF for fixing the image on the recording material P. The image forming unitA includes a photosensitive drum, serving as an image bearing member, a charge unit, a laser scanner, serving as an exposing unit, a developing unit, a cleaner, and a transfer member. The photosensitive drumis a photoconductor (electrophotographic photoconductor) formed in a drum shape. A configuration of the fixing unitF will be described below.

An image forming operation of the image forming apparatuswill be described. When a control unit of the image forming apparatus has received the image data, the image forming operation is started. When the image forming operation has been started, the photosensitive drumis rotatably driven, and a surface of the photosensitive drumis uniformly charged by the charge unit. The laser scannerirradiates the photosensitive drumwith a laser beam in accordance with a video signal generated based on the image data, and performs an exposure step of writing an electrostatic latent image on the surface of the photosensitive drum. The developing unitperforms a development step using the toner as the developer, and visualizes the electrostatic latent image as the image (toner image).

Concurrently with the operation described above, the recording material P stored in a cassettein an interior of an image forming apparatus body is fed one sheet at a time by the rotation of a feed roller. The recording material P is conveyed to a transfer nip Nt (transfer portion) formed between the photosensitive drumand the transfer memberby a registration roller. The image which has been formed on the photosensitive drumand conveyed to the transfer nip Nt by the rotation of the photosensitive drumis transferred onto the recording material P at the transfer nip Nt.

The recording material P which has passed through the transfer nip Nt is sent to the fixing unitF via a conveyance guide. By heating the image on the recording material P, the fixing unitF fixes the image on the recording material P. The recording material P which has passed through the fixing unitF is discharged to an exterior of the apparatus body by a sheet discharge roller, and stacked on a tray.

The image forming apparatusdescribed above is an example of image forming apparatuses. It is acceptable that the image forming unitA is an image forming apparatus of an intermediate transfer system in which the image formed on the image bearing member is transferred onto the recording material via an intermediate transfer member such as an intermediate transfer belt. Further, it is acceptable that the image forming unitA is configured to be capable of forming monochromatic images of respective colors on a plurality of photosensitive drums using a plurality of colors of toner, and configured to be capable of forming a color image by superimposing the monochromatic images of the respective colors on the intermediate transfer member or the recording material.

Next, an overview of the fixing unitF of the present embodiment will be described.is a schematic diagram illustrating a cross section of the fixing unitF.

Hereinafter, rotational axis directions of a fixing filmand a press rollerare referred to as a longitudinal direction Dof the fixing unitF or simply the longitudinal direction D. The longitudinal direction Dis a longitudinal direction (direction of the generatrix) of the fixing filmhaving a tubular shape. Further, the longitudinal direction Dof the fixing unitF is a direction (width direction of the recording material) perpendicularly intersecting with a conveyance direction of the recording material at a fixing nip Nf. Further, the longitudinal direction Dof the fixing unitF is substantially the same direction as a main scanning direction at a time of image formation in the image forming unitA.

Further, a circumferential direction Dof the fixing filmis a direction circulating along a surface of the fixing filmin a direction perpendicularly intersecting with the longitudinal direction D. In a case where the fixing filmis assumed to be in a cylindrical shape, the circumferential direction Dcan be a direction along a virtual circle having its center at a virtual rotational axis X of the fixing film. The rotational axis X is a straight line extending in the longitudinal direction Dalong a geometric center of the fixing filmwhen viewed in the longitudinal direction D.

As illustrated in, the fixing unitF includes the fixing film, serving as a tubular heating rotary member, a nip formation member, and a press roller, serving as a facing member (pressing member). Further, the fixing unitF includes a magnetic core, serving as a magnetic body, and an exciting coil, serving as a magnetic field generating member. All of the fixing film, the magnetic core, the press roller, and the nip formation memberare members elongated in the longitudinal direction D, and a dimension of each member in the longitudinal direction D(longitudinal width) is longer than a maximum width of the recording material P on which the fixing unitF can fix the image. Hereinafter, a passing area, in which the maximum width recording material P passes at a time of passing through the fixing unitF, in the longitudinal direction Dis referred to as a sheet passing portion or a sheet passing area, and an outside area of the sheet passing portion in the longitudinal direction Dis referred to as a non-sheet passing portion or a non-sheet passing area.

The nip formation memberis made of a heat resistant material such as a heat resistant resin, and is inserted into an inner space of the fixing film. The nip formation memberfaces the press rolleracross the fixing filmin a vertical direction perpendicularly intersecting with both of the longitudinal direction Dand the conveyance direction of the recording material P. Part of a surface of the nip formation memberof this example, on a side of the press roller, is formed as a flat surface portionextending in the longitudinal direction Dand the conveyance direction of the recording material P. The fixing nip Nf is formed between the flat surface portionof the nip formation memberand the press roller.

The press rollerincludes a core metalan elastic layerformed on an outer circumferential surface of the core metaland a release layerformed on an outer circumferential surface of the elastic layerAn outside diameter of the press rollerin this example is 30 millimeters (mm).

A support configuration of the fixing unitF will be described. Both end portions of the nip formation memberin the longitudinal direction Dare supported by a frame of the fixing unitF via flange members, described below. The frame of the fixing unitF is fixed to a frame of the image forming apparatus. A shaft portion of the core metalof the press rolleris supported, via bearings, in a manner rotatable with respect to the frame of the fixing unitF and movable with respect to the nip formation memberin the abovementioned vertical direction. The press rollercomes into pressure contact with the nip formation memberby an urging force of an urging member such as a spring. In this example, the bearings at both sides of the press rollerin the longitudinal direction Dare pressed by a pressing force of approximately 196 newtons (N) to 392 N (approximately 20 kilogram-force (Kgf) to 40 (Kgf) in terms of a total pressure (sum). Thereby, the elastic layerof the press rolleris elastically deformed, so that the fixing nip Nf in which surfaces of the fixing filmand the press rollercome into contact with each other with a predetermined width in the conveyance direction of the recording material is formed.

Next, the fixing filmof this example will be described. It is possible to form the fixing filmin the tubular shape with a diameter of 10 mm to 100 mm. An outside diameter of the fixing filmof this example is 30 mm. The fixing filmis made of a material having flexibility and heat resistance.

Cross-sectional views of the fixing filmare illustrated in.are transverse sections of the fixing film.is a longitudinal section of the fixing film. A layer configuration of the fixing filmand a pattern of a conductive layer are illustrated in the cross-sectional views in. To be noted, for the fixing filmand its components, a cross section cut by an imaginary plane perpendicular to the longitudinal direction Dis referred to as the transverse section, and a cross section cut by an imaginary plane parallel to the longitudinal direction Dis referred to as the longitudinal section.

As illustrated in, the fixing filmhas a structure in which a base layerthe conductive layera protective layeran elastic layerand a release layerare sequentially formed from an inner circumferential side to an outer circumferential side. An inner surface of the base layeris an inner circumferential surface of the fixing film, and an outer surface of the release layeris an outer circumferential surface of the fixing film.

As illustrated in, the conductive layerincludes a plurality of segments(divided conductors, conductive elements) arranged in a row in the longitudinal direction D. Each segmentcontinues over the entire circumference of the fixing filmin the circumferential direction D. That is, the conductive layerincludes circular shape (ring shape) elements.

The segmentsincluded in the conductive layerare electrically separated from each other with respect to the longitudinal direction D. In other words, the conductive layeris configured such that conductive materials included in the conductive layerare electrically separated from each other in the longitudinal direction D. In this example, the plurality of segmentsare electrically insulated from each other by disposing the segmentsadjacent to each other at predetermined intervals. That is, the conductive layerintermittently exists in the longitudinal direction D. To be noted, it is acceptable to dispose the plurality of segmentsclosely adjacent to each other.

In this example, an occupying ratio of the conductive layeris different depending on a position in the longitudinal direction D. In particular, presence or absence of the segmentsof the conductive layeris different between a central area A(first area) of the fixing filmpositioned in a central portion in the longitudinal direction Dand end areas A(second area) positioned on both outside of the central area Aand on end portions of the fixing film. An arrangement pattern of the segmentsand its action will be described below.

is the transverse section of the fixing filmillustrating an area in the longitudinal direction D(hereinafter referred to as a heat generating area) in which any one of the segmentsof the conductive layerexists.is the transverse section of the fixing filmillustrating an area in the longitudinal direction D(hereinafter referred to as a non-heat generating area) in which the segmentsof the conductive layerdo not exist.

A substance which is non-magnetic and has a high volumetric resistivity and excellent heat resistance is suitable for a material of the base layerSuch a substance includes, for example, the heat resistant resin such as polyimide (PI) and polyamideimide (PAI), a fiber reinforced resin such as carbon fiber reinforced plastics (CFRP) and a glass fiber reinforced resin (GFRP), and the like. In a case of using the heat resistant resin, the thickness of the base layeris preferably a thickness with which the strength of the fixing film, sliding properties of the fixing nip Nf, and the rotational stability of the fixing filmare easily obtained, and, for example, thicknesses of 20 to 200 micrometers (μm) are suitable. In this example, the base layer is formed of the PI, and the thickness is set at 50 μm.

For a material of the conductive layerfor example, metal having a low volume resistivity, such as gold, silver, copper, iron, platinum, tin, stainless steel, titanium, aluminum, and nickel, are suitable. In this example, copper is used as the material of the conductive layerand the thickness is set at 3 μm. Further, in this example, the width and thickness of each conductive layerin the longitudinal direction Dare set to be constant

An example of a method for forming the conductive layerwill be described. A coating film is formed by preparing paint containing a microparticle of the abovementioned metal and a polyimide precursor solution and, then, coating an outer surface of the base layerwhich has been prepared in advance, with the abovementioned paint in a manner of blade coating, screen printing or the like. In the coating process, by a common technique (such as a masking process), dividing portions (uncoated portions) dividing the segmentsinto each other are formed in portions corresponding to the non-heat generating area so as to form the segmentsat the predetermined intervals in the longitudinal direction D. Thereafter, the coating film described above is gradually heated and dried to and at about 300° C. to 500° C. so as to progress an imidation, so that the segmentsare formed and strongly adhered to the base layer. Besides the method described above, it is acceptable to form the segmentsby a technique such as laser etching or chemical etching after having plated the outer surface of the base layerwith the metal.

The protective layeris formed on an outer circumferential side of the conductive layerThe protective layerprotects the conductive layerAs with the base layera substance which is non-magnetic and has high volume resistivity and excellent heat resistance is suitable for a material of the protective layerSuch a substance includes, for example, the heat resistant resin such as the polyimide (PI) and the polyamideimide (PAI), the fiber reinforced resin such as the carbon fiber reinforced plastics (CFRP) and the glass fiber reinforced resin (GFRP), and the like. For the protective layerthicknesses of 20 to 200 μm which are the thicknesses with which the rotational stability of the fixing filmis easily obtained is suitable. In this example, the protective layeris formed of the PI, and the thickness is set at 50 μm.

The elastic layeris formed on an outer circumferential side of the protective layerThe elastic layeris formed of a heat resistant elastic body such as a silicone rubber. In this example, the elastic layeris formed of a good thermal conductivity silicone rubber with a thickness of 200 μm.

The release layeris formed on an outer circumferential side of the elastic layerThe release layerreduces the adhesion of the toner onto the surface of the fixing filmand the occurrence of image defects. A material which is excellent in non-adhesiveness is suitable for the release layerand it is possible to use a fluororesin. For example, a perfluoroalkylvinylether (PFA), a polytetrafluoroethylene (PTFE), a tetrafluoroethylene-hexafluoropropylene (FEP), or a tetrafluoroethylene-ethylene (ETFE) can be used. In this example, the PFA with a thickness of 15 μm is used for the release layer

Here, as illustrated in, the layer configuration of the fixing filmin the non-heat generating area is different from the heat generating area (refer to) in respect of the absence of the conductive layerThat is, in the non-heat generating area, the fixing filmincludes, from the inner circumferential side to the outer circumferential side, the base layerthe protective layerthe elastic layerand the release layer

Next, a configuration for generating a magnetic field so as to allow the fixing filmto generate heat will be described. As described above, the fixing unitF includes the magnetic coreand the exciting coil(refer to) disposed in the inner space of the fixing film.

is a perspective view (schematic diagram) illustrating a positional relationship among the fixing film, the magnetic core, and the exciting coil. The magnetic corehas a cylindrical shape, and secured substantially to the center in the fixing filmwith a securing member, not shown. The magnetic coreacts as a member which induces a magnetic field line (magnetic flux) of an alternating magnetic field generated by the exciting coilto the interior of the fixing filmand forms a path (magnetic circuit) of the magnetic field line.

The magnetic coreis preferably formed of a material that has a small hysteresis loss and a high relative permeability. As a material of the magnetic core, a ferromagnetic material including a high permeability oxide or alloy material, such as a sintered ferrite, a ferrite resin, an amorphous alloy, or a permalloy is preferred. Further, it is preferred to enlarge the cross-section of the magnetic coreas much as possible to the extent that a diameter of the magnetic corecan be fitted into the interior of the fixing film. In this example, the sintered ferrite with a diameter of 15 mm is used. The shape of the magnetic coreis not limited to the cylindrical shape, and it is possible to select a prismatic shape and the like.

In this example, the magnetic coreis disposed only in the interior of the fixing film, and forms an open magnetic circuit. As a modified example, it is acceptable to dispose a member which forms the magnetic circuit also in the exterior of the fixing film. Further, it is acceptable to form a closed magnetic circuit by the magnetic circuit forming member described above and the magnetic core.

The exciting coilincludes a helical portion L in which a single-conductor wire of a copper wire rod with a diameter of 1 to 2 mm coated with the heat resistant polyamideimide is wound over the magnetic corein a helical shape with a number of windings of approximately 10 to 30. An axis of the helical portion L is substantially parallel to the rotational axis X of the fixing film. Further, the magnetic coreover which the helical portion L is wound overlaps the rotational axis X.

To be noted, as described above, a dimension (longitudinal width) of the magnetic corein the longitudinal direction Dis longer than the maximum width of the recording material P on which the fixing unitF can fix the image. The magnetic coreforms the magnetic circuit substantially over the whole length of the fixing filmin the longitudinal direction D. It is suitable that an extension range of the magnetic corein the longitudinal direction Dincludes the central area Adescribed above. Further, it is suitable that the extension range of the magnetic corein the longitudinal direction Dincludes an area where the segmentsof the conductive layerare disposed. Further, it is suitable that the extension range of the magnetic corein the longitudinal direction Dincludes the sheet passing portion, and acceptable that the extension range of the magnetic corein the longitudinal direction Dincludes the whole length of the fixing film.

Power supply contact portionsandwhich are both ends of the exciting coilare electrically coupled to a high frequency converter, serving as an alternating current generation circuit. Based on a command from a control circuit, the high frequency convertersupplies a high-frequency current (alternating current) to the exciting coil. The high-frequency current flowing through the helical portion L of the exciting coilgenerates the alternating magnetic field around the fixing film.

With reference to, a heat generation principle of the fixing filmwill be described.are schematic diagrams illustrating magnetic fields (Bin, Bout) generated by the exciting coiland electrical currents induced in in the conductive layerof the fixing film.illustrates the transverse section of the fixing filmand the like, andis a perspective view illustrating the fixing film. To be noted, for the sake of simplicity, the protective layerthe elastic layerand the release layerare not illustrated in.

In, the magnetic core, the exciting coil, and the conductive layerare concentrically positioned from the center of the fixing film. The magnetic field line Bin toward the depth direction inand the magnetic inline Bout toward the front direction inare respectively illustrated by an arrow-tail symbol and arrow-head symbol.

A moment when the electrical current is increasing in the exciting coilin an arrow I direction inis considered. In this case, the magnetic field line Bin toward the depth direction inis formed in the inner space of the fixing filmmainly through the magnetic core, and the magnetic field line Bout returning in the front direction in an outer space of the fixing filmis formed. When the magnetic field represented by the magnetic field lines described above is formed, an induced electromotive force is generated over the entire circumference of each segmentof the conductive layerin the circumferential direction Dso as to offset the magnetic field, and the electrical current circulating in each segmentflows (hereinafter, this electrical current is referred to as a circulation current J).

Since the induced electromotive force is generated in a circulating direction of the conductive layerthe circulation current J uniformly flows in the inside of the conductive layerThen, since the magnetic field generated by the exciting coilrepeats generation/extinction and a direction reversal by a high frequency current, the circulation current J flows in a manner of repeating the generation/extinction and the direction reversal in synchronization with the high frequency current. When the electrical current flows in the conductive layerthe Joule heat is generated in accordance with electrical resistance of the material (for example, metal) of the conductive layer

The magnetic field lines Bin and Bout of the magnetic field generated by the exciting coilare substantially parallel to the longitudinal direction D, and directions become opposite to each other in the inside and the outside of the fixing film. Therefore, the circulation current J flows in the circumferential direction Dof the fixing film. As illustrated in, the circulation current J is generated in each of the electrically separated segmentsincluded in the conductive layer

As described above, in the fixing filmof this example, because the high frequency current is made to flow in the exciting coil, the circulation current J, serving as an induced current, flows in each of the segmentsof the conductive layerSince the circulation current J flows, the conductive layergenerates the heat.

Using, an operation of the fixing unitF will be described. When an image forming operation has been started, in synchronization with a predetermined timing, the fixing unitF starts the induction heating of the fixing filmby the heat generation principle described above. The predetermined timing has been set beforehand so as to make it possible to heat the fixing filmto a target temperature suitable for the fixing before the first recording material P reaches the fixing nip Nf. In conjunction with the start of heating the fixing film, the press rolleris rotatably driven by a motor, not shown, and rotates in an arrow Rp direction. The fixing filmrotates in an arrow Rf direction by following the press rollerby a friction force received from the press roller. In the fixing nip Nf, the fixing filmpasses through a gap between the flat surface portionof the nip formation memberand the press roller.